Photographic bleach composition



United States Patent PHOTOGRAPHIC BLEACH COMPOSITION Donald J. Kridel, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey N0 Drawing. Application March 30, 1956 Serial No. 574,989

2 Claims. (Cl. 96--60) This application relates to color photography and particularly to the removal of silver images in color photography.

In photographic color processes, such as those in which a colored image is formed by development with a primary aromatic amino developing agent in the presence of a coupler compound, the silver images formed in the development are generally present in the emulsion layer after the dye images are formed. These silver images are generally removed by converting them to a silver salt which is soluble or which is removed by hypo. A bath of this type containing potassium ferricyanide and potassium bromide is disclosed in Mannes, Godowsky, and Wilder U. S. Patent 2,252,718, granted August 19, 1941.

A requisite of ferricyanide and bromide bleach baths for certain processes is that the pH level be controlled. To achieve this control, buffering components such as boric acid and borax are added to the bleach composition. It has been found that if a bleach mixture is preprepared from potassium ferricyanide, potassium bromide, ortho boric acid and borax, the mixture tends to decompose on storage. The mixture decolors, and upon dissolving in water, gives a greenish-blue solution instead of the normal yellow color. This color is due to ferric ferrocyanide, initially in coloidal suspension, which co agulates and deposits as a blue-green stain on the photographic materials being processed.

It is therefore an object of the present invention to provide a novel bleach composition and method for bleaching silver images in the presence of color developed dye images in a photographic emulsion layer. A further object is to provide a novel method for converting silver images to a silver salt without destroying the dye image present in the emulsion layer. A still further object is to provide a bleach composition which has good keeping properties. Other objects will appear from the following description of my invention.

These objects are accomplished by substituting boric anhydride for all or a portion of the ortho boric acid in a bleach composition comprising potassium ferricyanide, potassium bromide, ortho boric acid and borax.

In the composition prepared according to my invention, the boric anhydride content may be from 0.1% to about based on the weight of the dry ingredients of the composition. The bleach bath is prepared for use by dissolving the dry composition in water.

The bleach baths employed according to my invention may be used in any process in which silver images are present in a photographic layer together with dye images. The dye images may be those formed by color development as described in Mannes, Godowsky and Wilder U. S. Patent 2,252,718; Mannes and Godowsky U. S. Patents 2,113,329 and 2,304,940; or Jelley and Vittum U. S. Patent 2,322,027. These dyes are of the azomethine, indoaniline or indophenol type. The dyes 2,843,482 Patented July 15, 1958 may also be azo dyes such as those used in the silver dye bleach process of color photography. After all of the steps of color processing, the photographic layer or element is treated with the bleach bath of my invention followed by hypo to remove the silver salts formed by the bleach bath.

The bleach composition of my invention may also contain sodium nitrate to inhibit corrosion of steel vessels or parts of apparatus with which the bleach solution comes in contact.

The following examples illustrate compositions which are prepared according to my invention:

EXAMPLE 1 Grams Potassium ferricyanide 20 Potassium bromide 10 BoraX-IOH O 1 Ortho boric acid 5 Boric anhydride 3 For use, mix with water to form 1 liter of solution.

EXAMPLE 2 Part A Grams Sodium nitrate 30 Part B Potassium ferricyanide 15 Potassium bromide 5.5 Borax-5H O 0.5 Ortho boric acid 2.5 Boric anhydride 1.4 For use, mix with water to form 1 liter of solution.

EXAMPLE 3 Part A Grams Sodium nitrate 26 Part B Potassium ferricyanide 29 Potassium bromide 12 Borax-5H O 1 Ortho boric acid 7.5 Boric anhydride 4.22

For use, mix with water to form 1 liter of solution.

It will be understood that the examples included herein are illustrative only and that my invention is to be taken as limited only by the scope of the appended claims.

What I claim is:

1. A dry powder bleach composition which, when dissolved in water, is capable of converting to silver salt only the silver images in a photographic layer containing both silver and dye images, comprising potassium ferricyanide, potassium bromide, borax and boric anhydride.

2. A dry powder bleach composition which, when dissolved in water, capable of converting to silver salt only the silver images in a photographic layer containing both silver and dye images, comprising potassium ferricyanide, potassium bromide, borax, ortho boric acid and from 0.1% to 10%, based on the weight of the mixture, of boric anhydride.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,843,482 July 1.5 1958 Donald. J, Kridel It is hereby certified that error appears in the printed apecification of tlie' above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 3% for "coloidal" read oolloidal column. 2,, line 58, before "capable" insert ie Signed and sealed this 14th day of October 1958.,

(SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

1. A DRY POWDER BLEACH COMPOSITION WHICH, WHEN DISSOLVED IN WATER, IS CAPABLE OF CONVERTING TO SILVER SALT ONLY THE SILVER IMAGES IN A PHOTOGRAPHIC LAYER CONTAINING BOTH SILVER AND DYE IMAGES, COMPRISING POTASSIUM FERRICYANIDE, POTASSIUM BROMIDE, BORAX AND BORIC ANHYDRIDE. 